1. Field of the Invention
The present invention relates generally to a punching unit for perforating sheet metals and other sheet materials and pertains more particularly to a multiple tool holding unit which can hold various punches and dies, both large and small, to be used with presses.
2. Description of the Prior Art
It is well known that perforating sheet materials such as sheet metals is carried out by a punching unit which has a punch or upper tool and a die or lower tool and is mounted on the table of a press just beneath the ram thereof. A typical type of the conventional punching unit is of a gnerally C-shaped construction which has an upper arm for holding the punch or upper tool and a lower arm for holding the die or lower tool and forms between the upper and lower arms a throat or opening into which the material to be perforated is to be inserted. Since punches and dies for punching holes of a certain range of sizes are so constructed that their portions to be held by the punching unit are all equal in size and shape, the punching unit can hold different punches and dies for punching holes of a certain range of sizes to be used to punch as wide a range of holes in size as possible.
It has been, however, a serious disadvantage with the conventional punching unit that the range of sizes of holes to be punched thereby is limited. It is, therefore, necessary to provide a larger punching unit for punches and dies for punching larger holes and a smaller one for punches and dies for smaller holes. Accordingly, it has been required to change the larger and smaller punching units with each other when it is desired to punch larger holes after punching smaller holes, and vice versa. This job has been very troublesome and time-consuming and also dangerous since the punching units are very heavy and are to be placed on the high work table of a press.
Another disadvantage with the conventional punching unit has been the fact that is is very troublesome to replace punches and dies with others for desired sizes and shapes even when it is not needed to replace the whole punching unit with another larger or smaller one. It has been often required to pull forward the whole punching unit on the table of the press to change punches and dies.
Although there have been some means to overcome the abovementioned disadvantages, they have been costly, and it also has been often required to make a special machine in order to incorporate such a means.